This invention relates to graded-index polymer optical rods and fibers.
Optical fibers are used throughout the telecommunication industry for high speed transmission of data over large distances. Typically, the optical fibers are single-mode fibers made from inorganic glasses. The material properties of these glasses impose an upper limit of about 125 .mu.m on the diameter of the fiber for a fiber having a reasonable flexibility. Because of these small diameters, splicing and interconnecting of such fibers is complex and time-consuming. As a result, single-mode glass fibers are inappropriate for short-haul data transmission applications, such as local area networks (LANs) or fiber to the home (FTTH), where multiple connections are required.
Polymer optical fibers (POFs) are an attractive alternative to glass fibers, because of their low cost, ease of handling, and good flexibility. Even at large diameters, POFs are flexible enough for efficient fiber splicing and beam insertion. The principal drawbacks of large-diameter POFs is the problem of modal dispersion and hence limited bandwidth.
Most POFs used in communication systems are of the step index (SI) type, i.e., they have a refractive index change at the core-cladding interface. Modal dispersion limits the bandwidth in most SI POFs to about 100 Mb/sec. This is too low for many telecommunication applications, such as, fiber distributed data interface (FDDI), synchronous digital hierarchy (SDH), and broad band integrated services digital network (B-ISDN). For example, the required bandwidth for current network applications such as Asynchronous Transfer mode (ATM), Fiber Channel and Ethernet are up to 1062 Mb/sec, with an interest in scaling these bandwidths to more than 4 Gb/sec.
Modal dispersion can be minimized by fabricating a POF with a varying refractive index profile along the transverse dimension of the POF, i.e., fabricating a graded-index (GI) POF. Typically, the GI POFs have a refractive index profile that varies quadratically along the radial dimension of the POF, with the refractive index being the largest at the center of the POF.